In addition to the required capacity, applications of secondary data storage systems can be broadly characterized in terms of required access time, data transfer rates, and allowed volume and power dissipation. For example, most general computing applications, such as transaction processing, require both fast access and data rate and are well served by hard disk drives. The hard disk industry has increased the capacity of non-removable disk drives every year to satisfy the demands of the PC industry. Unless major changes occur over the next decade in the personal computer market, present application pull is expected to continue both in terms of capacity and access time requirements. Most people believe that future computer applications will continue to utilize as much capacity as can be made available at a reasonable price.
On the other hand image file storage (still images as well as video) applications require very low cost, high capacity storage media combined with fast data transfer rates. These applications are less sensitive to access times. Presently, removable storage devices including "digital versatile disks" satisfy these requirements and serve this category of applications.
In contrast to non-removable systems, for removable storage, yearly increases in performance are not necessarily desirable. This is because removable storage is tightly coupled with standards that are established for compatibility purposes. Removable storage manufacturers offer a capacity entry point that is usable for the desired applications. As indicated in Fig. 7.1, during the next decade it is expected that video applications will drive the removable storage consumer market. HDTV quality video disks, depending on the compression algorithms, will require about 15 GB for 2 hours of video. An erasable disk with a capacity of 36 GB or more would be able to store more than 4 hours with HDTV quality and more than 12 hours with standard definition TV quality and could be used as video-tape replacement. With upcoming personal level consumer applications such as video-mail, 3D video and server applications including electronic medicine and electronic digital libraries, removable storage applications could use capacities exceeding a terabyte per platter. Typically this class of applications will require about 1 Gb/s data transfer rates but moderate access times.
Fig. 7.1. Potential evolution of application requirements for removable storage.
A third category of applications concerns portable and handheld devices that place more importance on volume and power dissipation considerations. Typical applications include compact storage systems for camcorders, personal digital assistants and communicators. Within the next decade, these applications will require about 50 GB capacity and reasonably fast access times (microseconds) and transfer rates (100 Mb/s) within very small volumes with power dissipations not exceeding a few milliwatts. Miniaturized disk drives, solid state disks or probe storage may serve this category of applications in the future.
It was the strong belief of this panel's Japanese hosts in general that the performance of data storage systems during the next decade will not be limited by a lack of applications pull but will rather be constrained by the capabilities of technologies in hand.
In the previous chapter, projections were made for areal densities that could be possible with more conventional technologies. As can be seen from Fig. 7.2, it will be increasingly difficult to exceed 100 Gb/in2 or 100 GB/disk (12 cm diameter) with conventional techniques. Based on roadmaps derived from the panel's visit in Japan, presented in earlier chapters, a window of opportunity is expected to open by 2005 for alternative storage technologies. Thus, it is important to study the potential performance characteristics of new emerging technologies and understand their application potentials.
Fig. 7.2. Estimates for possible areal densities that may be reached by various conventional techniques.